Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a sheet.
Description of the Related Art
Generally, when an image is transferred on both sides of a sheet, in the image forming apparatus, a transferring portion transfers an image onto a first surface of a sheet, the sheet is conveyed such that the direction of the sheet is converted and then inverted by an inverting mechanism. The sheet is resupplied to the transferring portion so that the image is transferred onto a second surface.
Further, the image forming apparatus has a function that discharges the sheet where an image is transferred onto the first surface to the outside of the apparatus or inversely discharges the sheet so as to align a page and includes a plurality of conveying paths whose discharge ports are arbitrarily converted.
Many of the image forming apparatuses have a configuration where a downstream in a sheet conveyance direction of a discharging portion in a sheet conveyance direction is disposed outside the apparatus and are easily affected by an atmospheric temperature. A sheet to which a toner image is transferred and which is heated and pressurized by a fixing device is conveyed to the discharging portion while having a predetermined heat.
If a conveying guide which forms a conveying path is formed of a metal plate in order to extend a life-span, in some cases, a moisture which is discharged from a sheet which passes through the fixing device is cooled by the conveying guide of the discharging portion to cause dew condensation that water droplets are attached onto the conveying guide. If a sheet is conveyed again onto the conveying guide in which the dew condensation occurs, the water droplets are attached from the conveying guide onto the sheet and thus a conveyance resistance between the sheet and the conveying guide is increased to stop the sheet. Therefore, a sheet jam may occur.
As for this problem, in Japanese Patent Laid-Open No. 2001-316018, in a diverging portion which allows a sheet to be selectively conveyed into conveying paths, a venting hole is provided in a switching member that diverges the conveying path and air is blown from the lower part of the switching member by an air-blowing device. Therefore, humid air around the diverging portion is discharged outside the apparatus without being held therein. Accordingly, the occurrence of the dew condensation is suppressed without cooling the moisture discharged from the sheet by the conveying guide of the discharging portion.
According to the technology disclosed in Japanese Patent Laid-Open No. 2001-316018, the occurrence of the dew condensation which occurs during conveying the sheet can be suppressed. However, it is difficult to suppress the dew condensation which occurs at the time of post-processing the sheet jam after the sheet jam occurs around the diverging portion when an image is formed on a plurality of sheets.
When a sheet jam occurs around the diverging portion at the time of forming an image on a plurality of sheets, in the discharging portion, a sheet which is fixed by the fixing device and has a predetermined heat remains around the diverging portion. Therefore, even though air is blown from the air-blowing device, the discharging of the moisture, which is discharged from the sheet, from the switching member is hindered by the sheet.
Accordingly, the moisture is cooled by the conveying guide of the discharging portion so that the dew condensation occurs in the conveying guide. If the sheet is conveyed again to the discharging portion in this state after the post-processing of the sheet jam, the conveyance resistance between the sheet and the conveying guide is increased so that the sheet jam occurs again. The sheet jam increases a temperature of the conveying guide of the discharging portion and the dew condensation continuously occurs until the conveying guide is at a temperature where the moisture discharged from the sheet is cooled so as not to be dew-condensed.
Meanwhile, when it is intended to increase image quality of the image forming apparatus and cope with the expanding of the kinds of available sheet media, it is difficult to mount the configuration disclosed in Japanese Patent Laid-Open No. 2001-316018 and it is further difficult to suppress the occurrence of the dew condensation.
If a venting hole is provided in the switching member which is disposed near the fixing device, there are a sheet surface having a rapid cooling speed which contacts with a portion of the switching member where the venting hole is not present in a width direction perpendicular to a conveyance direction of the sheet and a sheet surface having a slow cooling speed which faces the venting hole. For example, if a sheet such as a coat paper whose surface is coated is used, an image defect such as a gloss irregularity caused by a difference in cooling speed occurs on the sheet surface of the jammed sheet.
Therefore, it is required to form the conveying guide such as a switching member which contacts with the sheet immediately after the fixing device on a surface which does not have the venting hole. Since it is difficult to provide the venting hole, the humidity air easily remains so that the dew condensation easily occurs.
The present invention is contrived to provide an image forming apparatus that suppresses the occurrence of the dew condensation at the time of post-processing a sheet jam and prevents an additional sheet from being jammed.